The natural history, survival duration, and response to therapy in breast cancer is very diverse even within specific staging subgroups. Clinical factors, to a certain extent, have provided information regarding prognosis; however, biological factors which might enlighten us regarding mechanisms of progression are sorely lacking. Based on the observations of hematologic malignancies and preliminary results involving solid tumors, we predict that cytogenetic analysis should provide significant information regarding natural history and survival. The studies proposed will correlate chromosomal alterations with the clinical features of this disease and compare these changes with known prognostic factors.